This invention is related to an electrical alternator, of a type particularly adapted for use in motor vehicle applications including passenger cars and light trucks. These devices are typically mechanically driven using a drive belt wrapped on a pulley connected to the crankshaft of the vehicle's internal combustion engine. The belt drives a pulley on the alternator which rotates an internal rotor assembly to generate alternating current (AC) electrical power. This alternating current electrical power is rectified to direct current (DC) and supplied to the motor vehicle's electrical bus and storage battery.
While alternators have been in use in motor vehicles for many decades, today's demands on motor vehicle design, cost, and performance have placed increasing emphasis on the design of more efficient alternators. Today's motor vehicles feature a dramatic increase in the number of electrical on-board systems and accessories. Such electrical devices include interior and exterior lighting, climate control systems; and increasingly sophisticated power train control systems, vehicle stability systems, traction control systems, and anti-lock brake systems. Vehicle audio and telematics systems place further demands on the vehicle's electrical system. Still further challenges in terms of the output capacity of the motor vehicle's electrical alternators will come with the widespread adoption of electrically assisted power steering and electric vehicle braking systems. Compounding these design challenges is the fact that the vehicle's electrical system demands vary widely, irrespective of the engine operating speed which drives the alternator and changes through various driving conditions.
In addition to the challenges of providing high electrical output for the vehicle electrical alternator, further constraints include the desire to minimize the size of the alternator with respect to under hood packaging limitations, and its mass which relates to the vehicle's fuel mileage.
In addition to the need of providing higher electrical output, designers of these devices further strive to provide high efficiency in the conversion of mechanical power delivered by the engine driven belt to electrical power output. Such efficiency translates directly into higher overall thermal efficiency of the motor vehicle and thus into fuel economy gains. And finally, as is the case with all components for mass-produced motor vehicles, cost remains a factor in the competitive offerings of such components to original equipment manufacturers.
Enhanced efficiency of the alternator can be provided through various design approaches. The alternator uses a rotating rotor assembly, which creates a rotating alternating polarity magnetic field. This rotating alternating polarity magnetic field is exposed to an annular stator core assembly which closely surrounds the rotor assembly. Electrical conductor windings are embedded within the stator core assembly. A number of design challenges are presented with respect to the design and manufacturing of the stator core assembly which includes a stator core and the windings. The stator core has a series of radially projecting slots. Some alternator designs employ conventional wire conductors having a round cross sectional shape laced into the stator core winding slots. These round cross-sectional wires are nested against other turns of wire in the slots. The use of such round wire produces air spaces between adjacent turns of wire. This air space represents unused space in the cross section of the stator core. Electrical resistance through a solid conductor is related to its cross sectional area. Consequently, the air space between adjacent turns of a round wire stator represents inefficiency since that space is not being used to carry electrical current through the stator windings.
One improved design of stator core assembly uses stator windings formed of rectangular or square cross sectional wire. Such wire can be laced into the stator core winding slots in a very densely packed configuration. This allows larger cross sectional areas to be provided for the conductors, thus lowering the conductor's resistance. Reducing the stator core winding resistance improves efficiency. Such rectangular wire core designs are said to improve “slot space utilization”.
Although rectangular cross section wire for the stator core assembly provides the previously noted benefits, its use produces a number of design challenges. Rectangular cross section wire is more difficult to form and wind into the stator winding slots, since it is necessary to align the cross section to the slot dimensions.
Since the stator conductors are laced from the two axial ends of the stator core, they are looped at their ends to pass into the next appropriate winding slot. It is desirable to reduce the length or height of these end loops as a means of reducing the total length and therefore the internal resistance of the conductors.
Designers of stator assemblies further attempt to reduce or eliminate the need for providing electrical conductor terminations and connections in the stator assembly. The necessity to physically connect conductors in the stator core assembly adversely impacts cost and complexity of the manufacturing process. An advantageous design of an alternator stator assembly would enable the stator assembly to be readily adapted for various types of electrical connections and number of phases of produced alternating current. Automotive electrical alternators are often manufactured in a three-phase configuration with the phases connected in the familiar delta or Y connections. As mentioned previously, the alternating current output is later rectified and conditioned by downstream electrical devices.